Semiconductor power device with insulated gate formed in a trench, and manufacturing process thereof

Abstract

A semiconductor power device has a semiconductor body with a first conductivity type. A trench extends in the semiconductor body and accommodates an insulating structure, which extends along the side walls and bottom of the trench. The insulating structure surrounds a conductive region, arranged on the bottom of the trench, and a gate region, arranged on top of the conductive region, the conductive region and the gate region being electrically insulated by an insulating layer. A body region, with a second conductivity type, extends within the semiconductor body, at the sides of the trench, and a source region, with the first conductivity type, extends within the semiconductor body, at the sides of the trench and within the body region. The conductive region and the gate region are both of polycrystalline silicon but have different conductivities and doping levels so as to have different electrical characteristics such as to improve the static and dynamic behaviour of the device.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an insulated-gate semiconductor power device and to the manufacturing process thereof. More specifically, the invention relates to a power MOS device of the type comprising a trench used for insulating the gate region of the device (hereinafter indicated as power MOS device of the trench-gate type). [0003] The invention relates, in particular, but not exclusively, to a power MOS device or a device of the IGBT (Insulated-Gate Bipolar Transistor) type, and the following description is made with reference to this application field, with the only purpose of simplifying its exposition. [0004] 2. Description of the Related Art [0005] As is known, power MOS devices comprise a plurality of cells, each having a gate region adjacent to body and source regions. In the manufacturing process of trench-gate power MOS devices, the gate of the MOS structure is formed in each elementary cell of the d...

AI Technical Summary

Benefits of technology

[0009] The first problem (crowding of the electric-field lines) is currently solved by making the trench with a U-shaped profile, rounded at its bottom end. In this way, in fact, the resistance to breakdown of the device is improved.

[0012] the breakdown voltage of the device increases because the thick oxide layer performs the function of “field ring”, i.e., that of preventing crowding of the electric field lines at the bottom of the trench;

[0016] In particular, the solution that envisages a U-shaped thick oxide on the bottom of the trench provides better performance as regards the improvement of the breakdown voltage (higher values are obtained), while the second solution (thick oxide that completely fills the bottom of the trench) behaves relatively better in regard to parasitic capacitance.

[0017] One embodiment of the present invention provides a power device of the type referred to above that yields a better compromise as to the two above aspects so as to present a substantially improved behavior as regards both breakdown and parasitic capacitance.

[0018] In practice, to reconcile both the static aspect and the dynamic aspect of the device, the polysilicon region that fills the trench is divided into two parts with different physical and electrical characteristics. According to one embodiment of the invention, the bottom part is formed by a lightly doped polysilicon of a type opposite to the polysilicon of the top part (which forms the gate region) so as to function as an electrode with reverse biasing. In this way, the device maintains the breakdown gain of the known solution described above with U-shaped thick oxide and has an improved dynamic behaviour in so far as the bottom part of polysilicon can undergo depletion during switching and thus provides a minor contribution to the capacitance of the polysilicon region.

Problems solved by technology

On the other hand, this structure presents some problems.

Furthermore, as compared to a planar structure, there arises, given the same active area, a considerable increase in the area of the gate oxide, also in useless areas, where the channel is not formed, i.e., in those parts of the gate oxide that extend underneath the body region.

Images